What lore do you ignore?

[Lady_Silvermoon]

You're blurring two things here: someone having knowledge of the future, and what causes people to act.

If there's some higher-level embodiment of Fate in this story's universe that drives people to act in a certain way, then Venat is as much a puppet as the rest. She is not the controller of fates and doesn't have influence over what other people will do; she's simply relying on the sequence of events in which things will happen as she has been told they will.

And if there is no driving force of fate, then there is only a world shaped moment-by-moment by the decisions of the people living in it, and those people are in control of their own path at the time they are taking it, no matter whether someone from the past has knowledge that they will do it in future, and no matter whether someone in the future knows that it happened in history.

G'raha did not somehow magically decide to save the world because Venat knew he would; he made that decision for himself, and Venat has learned about it as "future history". That is all.

But without knowledge of "future history" you don't really have the choice to do anything differently. The only person that can choose to act differently is someone who knows what they did before and the results of their actions making Venat the only person with true agency in the FF14 universe. Everyone else is just following a script. We do what we do because it's what we've always done.

ETA: Actually that's not true. The WoL could also choose to act differently and chance the course of events because they also have knowledge of the future.